Ev value means: a quantity reflecting the degree of exposure. EV, the abbreviation of ExposureValues, is a quantity that reflects the degree of exposure. Initially defined as: the sensitivity is ISO 100, the aperture coefficient is F 1, and when the exposure time is 1 s, the exposure is defined as 0, and the exposure is reduced by one step (the shutter time is halved or the aperture is reduced by one step), and the EV+ 1. Increase exposure by one step (double shutter time or increase aperture by one step), EV- 1. The EV values corresponding to common exposure combinations are as follows (the sensitivity is ISO 100). If the sensitivity is ISO 100, if the aperture of F 1 1 is combined with the shutter time of1125s, the EV value when the exposure is just right is (7+7) 14. When the EV value is constant, different aperture and shutter time can be used for combination. For example, EV 14 can be F8 and 1/250S, or F 16 and 1/60S.